Police believe Sherie Lea James may have swallowed five of the tablets before suffering a fatal cardiac arrest.
And her heartbroken family believe the 15-year-old was more vulnerable because she had a liver transplant when she was just 20 months old.
Miss James went to a small house party on the night she died with a friend who also is believed to have taken the drugs but survived.
Miss James” weaker immune system – as a result of her liver transplant – may have caused her death when a fitter person would have lived.
As a tot, she had the country”s fastest ever liver transplant lasting just 45 minutes in July 2002.
Miss James was also taking medication to stop her body rejecting her liver and whenever she was ill it was “twice as bad and for twice as long” as everyone else, her heartbroken mum Sam James said.
The 43-year-old has urged teenagers to stay away from illegal substances.
She said: “I have lost my daughter and I will never get over that.
“If one good thing can come out of this I hope that kids think twice about taking drugs.
“If it makes one person think before taking something then I suppose that”s something I can take from it.”
The schoolgirl had been home three days from a holiday to Cornwall when she died in the early hours of September 1.
Miss James – who had originally planned to have a night in with her mum – hit the town with her new friend.
Her mother, of Basildon, Essex, added: “I dropped her off £20 and I said “you look amazing”. She said “I”m loving life”.
“I told her to slow down and she said “love you mum” and that was the last time I spoke to her.”
The two teens spent the evening at Lakeside shopping centre and then went to her friend”s house in Laindon, Essex.
But at some point that night they left and went to a 29-year-old”s one-bedroom flat in South Ockendon, Essex.
She sent a Snapchat message at 1.45am where she said: “Oh, where have I ended up.”
Six people were at the gathering – all of the men were considerably older than the teens, Ms James was told.
Cops alerted Ms James at 5.30am when she rushed to Basildon hospital
Paramedics broke her daughter”s ribs as they tried to save her life when she went into cardiac arrest.
But the teen was pronounced dead at the scene.
Her mother added: “I had three sons and I always wanted a girl and I got my girl and I almost lost her twice through cancer.
“We were so close. When she was a baby I used to sleep next to her and I”d get dangled in the tubes off her cot.
“My life will never been the same again without my beautiful girl. I just can”t see why she ended up in that situation?
“That is the tragedy. I would rather it would have been a car crash because I wouldn”t have to go through all of this.
“I haven”t been coping with anything since it happened. I can”t stop crying, I can”t sleep without tablets.
“I am dreading the funeral because it is for real. At the moment I don”t quite believe it”s real and she”s going to walk in the door but that will bring it home.”
A post-mortem has proved inconclusive.
A toxicology report is still being prepared which will reveal exactly which drugs she took.
The single mother is now determined that she is going to raise the £9,000 she needs to pay for a “celebrity” send off that Sherie-Lea wanted.
The other girl who overdosed has since made a full recovery.
A 19-year-old from South Ockendon and a 29-year-old from London have been arrested on suspicion of possession with intent to supply drugs.
The pair have been released on bail.